Frequency-fluctuating interference removed receiver

ABSTRACT

In order to efficiently and steadily remove a frequency-fluctuating interference wave, for instance, a leakage wave of a household electronic oven, intermixed into a received wave for communication, adaptively to the frequency deviation and the frequency fluctuation of the interference wave, a rejection band component included in the received wave applied onto a circulator, an output terminal of which is connected with a variable band rejection filter, is reflected from the output terminal on which impedance mismatch is caused by zero-impedance presented by the rejection filter on the basis of absorption of the input wave and applied to a detector through the circulator again, in response to a detection output of which a so-called peak-keeping control is effected on the variable band rejection filter for shifting the rejection band, so as to maximize the detection output of the detector adaptively to the frequency deviation and the frequency fluctuation of the interference wave.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a frequency-fluctuating interferenceremoved receiver for electromagnetic communication, provided forremoving a frequency-fluctuating interference wave, for instance, leakedfrom a household electronic oven, which is intermixed into a receivedwave, for instance, of the spread spectrum communication, the spectra ofwhich are spread over an allotted wide frequency range by doublymodulating a wave modulated in the base band through a code train,particularly so as to facilitate the efficient and steady removal of theinterfering wave, which is adapted to the frequency fluctuation of theinterfering wave.

2. Related Art Statement

For example, in the spread spectrum communication, generally, thespectra of the carrier wave modulated by base band information signal isspread over a wide frequency range by the double modulation effected bythe pulse code train and the like, so that, the deterioration of thedesired-to-undesired reception ratio of the received wave is not solarge and hence removal of the interfering wave has deliberately notbeen employed or no more than a simple band rejection through a fixedrejection band similar to that used in ordinary communication has beenemployed.

However, in the conventional case that the interfering wave is removedby employing the simple fixed band rejection filter, even for removingan interfering wave such as the leakage wave of the household electronicoven, which has a wide deviation and a great fluctuation of thefrequency over the allotted range, a conventional band rejection filterhaving a fixed wide rejection band corresponding to the deviation andfluctuation of the interfering frequency is used. Consequently, eventhough the spread spectrum communication is provided with the signalspectra spread over the allotted wide frequency range, the deteriorationof the quality of the demodulation output thereof is really caused bythe lack of signal spectra in the wide rejection band together with theremoval of the interfering wave.

SUMMARY OF THE INVENTION

An object of the present invention is to remove the aforesaidconventional difficulty and to provide a frequency-fluctuatinginterference removed receiver for communication which is arranged suchthat the interfering wave intermixed into the allotted frequency rangeof the electro-magnetic communication with frequency deviation andfrequency fluctuation over a wide range is efficiently and steadilyremoved through a variable narrow band rejection filter having thenarrowest rejection band possible which is automatically shifted bybeing adapted to the deviation and fluctuation of the interferingfrequency.

The frequency-fluctuating interference removed receiver forcommunication according to the present invention, wherein afrequency-fluctuating interference wave intermixed into a predeterminedfrequency range of a received wave for communication isfrequency-selectively removed, is featured by comprising a variablenarrow band rejection filter in which a narrow band component of aninput wave in said predetermined frequency range isfrequency-selectively absorbed, so as to present zero impedance withrespect to said narrow band component, and the remaining components arepassed through as the receiver input for communication, a detector inwhich said narrow band component is detected, a directionally deliveringdevice for delivering said received wave for communication to saidvariable narrow band rejection filter and for delivering said narrowband component reflected by impedance mismatch based on zero impedancepresented by said variable narrow band rejection filter to said detectorand a controlling circuit for controlling said variable narrow bandrejection filter so as to shift the rejection band of said filter onto aside on which the detection output of said detector is increased.

Consequently, in the frequency-fluctuating interference removed receiverfor communication according to the present invention, it is facilitatedto efficiently and steadily remove the interfering wave through thenarrowest possible rejection band automatically adapted to the frequencydeviation and the frequency fluctuation of the interfering wave andhence to further improve the desired-to-undesired reception ratioinherently favorable in the electromagnetic communication.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the invention, reference is made to theaccompanying drawings, in which:

FIG. 1 is a block diagram showing the fundamental arrangement of theessential portion of the frequency-fluctuating interference removedreceiver for communication;

FIG. 2 is a block diagram showing the fundamental arrangement of acontrolling circuit of the same; and

FIGS. 3A, 3B and 3C are cross-sectional views showing examples of avariable band rejection filter coupled with a micro-strip line and arectangular waveguide respectively and a circuit diagram showing anequivalent circuit of the same.

Throughout different views of the drawings, 1 is an input terminal, 2 isa circulator (a directional coupler), 3 is a variable band rejectionfilter, 4 is an output terminal, 5 is a detector, 6 is a controllingcircuit, 7 is a discriminator-controller, 8 is a sweeper, 9 is a memory,10 is a peak-keeping controller, 11 is a resonant device, 12 is amicro-strip line, 13 is a rectangular wave guide and 14 is a post.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described indetail by referring to accompanying drawings hereinafter.

In electro-magnetic communication, the frequency range allotted for thecommunication concerned is protected. However, frequently an interferingwave leaked from an electronic apparatus other than those used for thecommunication, for instance, from a household electronic oven, isintermixed into the frequency range allotted to the communicationconcerned. As a result, an impermissible interference is brought abouteven for spread spectrum communication which inherently has slightdeterioration of the desired-to-undesired reception ratio.

Consequently, in accordance with the present invention, afrequency-fluctuating interference removing apparatus having afundamental arrangement as shown in FIG. 1 is provided to precede thecommunication receiver, so as to efficiently and steadily remove theaforesaid frequency-fluctuating interference wave through a variableband rejection filter having the narrowest possible rejection bandadapted to the frequency deviation and the frequency fluctuation of theinterference wave.

In the frequency-fluctuating interference removing apparatus arranged asshown in FIG. 1, a received wave for communication is applied from aninput terminal 1 onto a variable band rejection filter 3 through amicro-strip line, or the like by way of a directional delivering device2 which consists preferably of a circulator or a directional coupler.The variable band rejection filter 3 is provided with a variablerejection band having a central frequency corresponding to the momentaryinterfering frequency within the allotted frequency range and with azero impedance at the momentary interfering frequency against thedelivering line impedance on the basis of absorption of an input wave.In other words, this filter 3 is a band rejection filter consisting, ina simple case, mainly of a serial resonant LC circuit, by whichinterfering frequency components within the predetermined frequencyrange are rejected, and through which remaining components within thesame frequency range are passed, so as to be taken out from an outputterminal 4 as an input for the communication receiver, and furthermorethe resonant frequency of which can be adjusted by any electrical means,for instance, by forming the aforesaid serial resonant LC circuit of avaractor. Consequently, it is preferable in practice that this variableband rejection filter 3 is formed of an adjustable resonant device suchas a magneto-static resonant device, the resonant frequency of which canbe adjusted through an applied direct magnetic field intensity, or adielectric resonant device provided with a varactor as a couplingelement, in a form of a bridged T-type band rejection filter, asdescribed later.

The rejection band components included in the input wave applied ontothe directional delivering device 2 such as the circulator, an outputterminal of which is connected with this variable band rejection filter3 are reflected from the output terminal on which impedance mismatch iscaused by the zero impedance presented by the rejection filter 3 andhence delivered to a detector 5 again by way of another output terminal,a detection output of which is applied onto a controlling circuit 6fundamentally arranged as shown in FIG. 2. In this controlling circuit6, under the control of a discriminator-controller 7 applied with thedetection output from the detector 5, a sweeper 8 generates a sweepingsignal consisting, for instance, of a sawtooth-shaped voltage, which isapplied on a control terminal of the variable band rejection filter 3through a memory 9 and a peak-keeping controller 10 successively, so asto control the driving voltage of the resonant frequency decidingelement of filter 3, for instance, the aforesaid varactor, such that thecentral frequency of the rejection band is repeatedly varied over theallotted frequency range of the communication concerned.

In this state of the swept band rejection, once any interfering waveintermixed into the allotted frequency range is caught by the variableband rejection filter 3, under the control of controlling signals formedin the discriminator-controller 7 each time in response to the detectionoutput of the detector 5, the voltage sweeping in the sweeper 8 isstopped and then the swept voltage at the instant of the interferencedetection is held in the memory 9.

In this state in which the swept voltage at the instant of theinterference detection is held in the memory 9, a peak-keepingcontroller 10 is driven such that the swept voltage is slightly deviatedin either of positive and negative polarities from the held voltage, soas to apply the optimum or peak-keeping control on the resonantfrequency deciding element of the variable band rejection filter 3.

That is, in the peak-keeping controller 10, a slight voltage deviated ineither of positive and negative polarities from a reference voltage, forinstance, zero voltage on the condition where the interference is notyet detected, is generated stepwise or continuously and then superposedon the held voltage at the instant of the interference detection, so asto be applied on the resonant frequency deciding element of filter 3. Inthis state, the polarity of the variation of the detection output levelof the detector 5, which is caused in response to the slight deviationof the aforesaid applied voltage, is discriminated by thediscriminator.controller 10. On this condition, in a case that thedetection output level of detector 5 is increased in response to theslight deviation of the applied voltage, the applied voltage is furtherdeviated in the same polarity, while, in the other case that thedetection output level is decreased in response to the slight deviationof the applied voltage, the applied voltage is further deviated in theopposite polarity.

As a result of the repetition of the aforesaid slight deviation of theapplied voltage, the detection output level which is increased ordecreased along a single peak characteristic curve can be always kept onthe peak or at least infinitely close to the peak.

In this connection, when the detection output level can not reach thepeak within the slight deviation of the applied voltage in thepeak-keeping controller 10, the aforesaid process of the interferencecatching is newly repeated under the control of thediscriminator.controller 7. In addition, in the case that the detectionoutput level is varied in response to the variation of the intermixedlevel of the interfering wave, the peak-keeping control according to theaforesaid process of the interference catching is effected with respectto the new intermixed level of the interfering wave.

Consequently, the interfering wave can be always caught adaptively tothe fluctuation of the frequency and the variation of the level thereof,so as to efficiently, steadily and readily remove the interfering wavethrough the variable narrow band rejection filter in spite of thefluctuation of the frequency and the variation of the level thereof.

The aforesaid preferable example of the variable band rejection filter 3will be further described below in detail.

It is difficult to realize a narrow band rejection filter having asufficiently narrow rejection band and an intense attenuation byemploying an ordinary lumped constant resonant circuit therefor.Accordingly, it is preferable to employ therefor a narrow band rejectionfilter arranged such that a resonant device consisting of aferro-magnetic or dielectric body is coupled with a distributed constanttransmission line, while resonant frequency components of anelectromagnetic wave on the transmission line are absorbed by anabsorbing resistive device.

That is, for instance, as shown in FIG. 3A, a plane PS of symmetry,which rectangularly crosses a micro-strip line 12 in a position intowhich the filter concerned should be inserted, should be supposed. Aresonant device 11 is formed of a ferro-magnetic material, for instance,a ferrite such as yttrium.iron.garnet or the like, or, of a dielectricmaterial in a pertinent size adapted to the resonant frequency.

In addition, an absorbing resistive element R is connected on one endwith the transmission line at the cross-point with the plane PS ofsymmetry through a coupling capacitor C and then, for example, isearthed on the other end.

In another example, as shown in FIG. 3B, the resonant device 11 isarranged in a rectangular waveguide 13 along an E wall face thereofsymmetrically with respect to the plane PS of symmetry, while a post,which is connected through the absorbing resistive element R with theouter wall face of the waveguide 13 in a position in which the plane PSof symmetry crosses the waveguide 13, is arranged such that a top endthereof is capacitively coupled with the waveguide 13 by being insertedthereinto.

The resonant device 11, which is coupled with the electromagnetic wavetransmission line by being arranged as described above, is operated as abridged T-type filter having an equivalent circuit as shown in FIG. 3C,and hence is resonant in odd mode with the electromagnetic wave on thetransmission line, so that an intense attenuation can be obtained at theresonant frequency by appropriately setting the resistance of theabsorbing resistive element R.

Particularly, the resonant device 11 formed of the ferro-magneticmaterial is resonant in the so-called magneto-static mode accompaniedwithout any electric field energy with a frequency adapted to theintensity of the applied direct current magnetic field on the basis ofthe precession of the electron spin, which is effected in the applieddirect current magnetic field. As a result, the device is operated as amagneto-static resonant device having an extremely high Q, so as torealize a band rejection filter which has a rejection band far narrowerthan that of the ordinary resonant circuit, and further which has only asmall effect upon the property of the electromagnetic wave in thefrequency range out of the rejection band.

In this connection, the direct current magnetic field required for theresonance in magneto-static mode can be readily applied on the resonantdevice 11 by arranging it along an arm of a rectangular yoke in whichmagnets are partially inserted, and the resonant frequency thereof canbe readily adjusted by appropriately setting the intensity of theapplied magnetic field in response to the current applied through coilswound on other arms of the yoke concerned.

As is apparent from the above discussion, an interfering wave havingsignificant dispersion and fluctuation of frequency such as a leakagewave of a household electronic oven, which is intermixed in the allottedfrequency range of the electro-magnetic communication, can beefficiently and steadily removed through the variable narrow bandrejection filter always adapted to such deviation and fluctuation offrequency, and hence even the excellent desired-to-undesired receptionratio which is inherent to the communication concerned is furtherimproved, providing an extremely remarkable effect.

What is claimed is:
 1. A frequency-fluctuating interference removedreceiver for communication, wherein a frequency-fluctuating interferencewave intermixed into a predetermined frequency range of an input wavefor communication is frequency-selectively removed, said receivercomprising:a variable narrow band rejection filter means having avariable rejection band and a control terminal for receiving a controlsignal that controls a central frequency of said rejection band, adetector means, a directional delivering means for receiving said inputwave, said delivering device being connected to said filter means andsaid detector means and providing said input wave to said filter means,said filter means frequency-selectively absorbing a narrow bandcomponent of said input wave in accordance with said rejection band, soas to present zero impedance with respect to said narrow-band component,and passing through other components of said input wave, said narrowband component corresponding to said frequency-fluctuating interferencewave, said delivering means receiving and delivering said narrow bandcomponent, reflected by impedance mismatch caused by zero impedancepresented by said filter means, to said detector means, said detectormeans providing an output having a variable level that is determined bysaid control signal applied to said control terminal of said filtermeans that controls said central frequency of said rejection band, and acontrol circuit means connected between said detector means and saidcontrol terminal of said filter means, for providing, in response tosaid output of said detector means, said control signal to said controlterminal of said filter means to shift said rejection band of saidfilter means in a direction which causes said output of said detectormeans to increase.
 2. A receiver as in claim 1, wherein said deliveringmeans is a circulator.
 3. A receiver as in claim 1, wherein said controlcircuit means includes a peak-keeping controller for providing saidcontrol signal to control said rejection band of said filter means, soas to maximize the output of said detector means.
 4. A receiver as inclaim 1, further comprising a transmission line through which said inputwave is transmitted from said delivering means to said filter means anda coupling capacitor, and wherein said filter means comprises a bridgedT-type band rejection filter including a resonant device, which ispositioned symmetrically with respect to a symmetry plane that issubstantially orthogonal to a longitudinal axis of a transmission linefor said input wave and is resonant relative to said input wave in theodd mode thereof, said bridged filter being coupled with saidtransmission line and further comprising an absorbing resistive element,which is coupled through said coupling capacitor with said transmissionline at the crossing point thereof with said symmetry plane, saidresistive element absorbing resonant frequency components of said inputwave transmitted on said transmission line to attenuate said input waveat the resonant frequency of said resonant device.
 5. A receiver as inclaim 4, wherein said resonant device comprises a magneto-staticresonant device in which a ferro-magnetic body is resonant in themagneto-static mode under a direct current magnetic field appliedthereon.
 6. A receiver as in claim 2, wherein said control circuit meansincludes a peak-keeping controller for providing said control signal tocontrol said rejection band of said filter means, so as to maximize theoutput of said detector means.
 7. A receiver as in claim 2, furthercomprising a transmission line through which said input wave istransmitted from said delivering means to said filter means and acoupling capacitor, and wherein said filter means comprises a bridgedT-type band rejection filter means including a resonant device, which ispositioned symmetrically with respect to a symmetry plane that issubstantially orthogonal to a longitudinal axis of a transmission linefor said input wave and is resonant relative to said input wave in theodd mode thereof, said bridged filter being coupled with saidtransmission line and further comprising an absorbing resistive element,which is coupled through said coupling capacitor with said transmissionline at the crossing point thereof with said symmetry plane, saidresistive element absorbing resonant frequency components of said inputwave transmitted on said transmission line to attenuate said input waveat the resonant frequency of said resonant device.
 8. A receiver as inclaim 3, further comprising a transmission line through which said inputwave is transmitted from said delivering means to said filter means anda coupling capacitor, and wherein said filter means comprises a bridgedT-type band rejection filter including a resonant device, which ispositioned symmetrically with respect to a symmetry plane that issubstantially orthogonal to a longitudinal axis of a transmission linefor said input wave and is resonant relative to said input wave in theodd mode thereof, said bridged filter being coupled with saidtransmission line and further comprising an absorbing resistive element,which is coupled through said coupling capacitor with said transmissionline at the crossing point thereof with said symmetry plane, saidresistive element absorbing resonant frequency components of said inputwave transmitted on said transmission line to attenuate said input waveat the resonant frequency of said resonant device.
 9. A receiver as inclaim 6, further comprising a transmission line through which said inputwave is transmitted from said delivering means to said filter means anda coupling capacitor, and wherein said filter means comprises a bridgedT-type band rejection filter including a resonant device, which ispositioned symmetrically with respect to a symmetry plane that issubstantially orthogonal to a longitudinal axis of a transmission linefor said input wave and is resonant relative to said input wave in theodd mode thereof, said bridged filter being coupled with saidtransmission line and further comprising an absorbing resistive element,which is coupled through said coupling capacitor with said transmissionline at the crossing point thereof with said symmetry plane, saidresistive element absorbing resonant frequency components of said inputwave transmitted on said transmission line to attenuate said input waveat the resonant frequency of said resonant device.
 10. A receiver as inclaim 7, wherein said resonant device comprises a magneto-staticresonant device in which a ferro-magnetic body is resonant in themagneto-static mode under a direct current magnetic field appliedthereon.
 11. A receiver as in claim 8, wherein said resonant devicecomprises a magneto-static resonant device in which a ferro-magneticbody is resonant in the magneto-static mode under a direct currentmagnetic field applied thereon.
 12. A receiver as in claim 9, whereinsaid resonant device comprises a magneto-static resonant device in whicha ferro-magnetic body is resonant in the magneto-static mode under adirect current magnetic field applied thereon.